The present invention relates to loudspeaker systems and in particular relates to a circuit for providing greater accuracy of sound reproduction by a loudspeaker.
It is well known that high fidelity loudspeakers have substantially improved in quality in recent years, yet they still suffer from persistent problems. Many of the problems are associated with component audio reproduction systems wherein differing power amplifiers may be utilized with a variety of differing loudspeakers and the different amplifiers and loudspeakers have distinct operating characteristics. A major problem associated with matching amplifiers and loudspeakers is associated with a tendency of a speaker to continue to mechanically move after being driven by electrical power delivered to the loudspeaker from the amplifier. As the speaker continues to move after the electrical power ceases, the speaker generates a voltage at the speaker""s input that travels along the circuit between the speaker and amplifier. The voltage is commonly referred to as back electromotive force (xe2x80x9cEMFxe2x80x9d), which is short circuited by a low output resistance of the amplifier. This short circuiting effect provided by the amplifier is referred to as electrical damping and has a braking effect upon continued movement of the loudspeaker. Amplifiers and connected speakers are referred to as having a specific xe2x80x9cdamping factorxe2x80x9d which is a ratio of speaker resistance to the low output resistance of the amplifier. For example, standard loudspeaker having a resistance of 8 ohms and an amplifier having a low output resistance or impedance of 0.20 ohms would have a damping factor of 40 (8.0/0.20). It is also well known that any resistance introduced between the amplifier and the loudspeaker lessens the damping effect of the amplifier. Different loudspeakers generate different back EMF, and hence it is difficult to match an amplifier to accommodate varying back EMF characteristics of a variety of loudspeakers.
Many efforts have been undertaken to better control the back EMF generated by loudspeakers. For example, U.S. Pat. No. 5,033,091 that issued on Jul. 16, 1991 to Bond shows usage of an unterminated connector with a pair of terminated connectors between positive and negative terminals of an amplifier and a loudspeaker, and in one embodiment the unterminated connector includes a rheostat to vary the resistance of the connector and thereby better match a particular speaker with an amplifier. Bond thereby endeavors to achieve a fixed damping of back EMF of a speaker by selecting electrical connectors having an unterminated connector that optimize a fixed, non-frequency variable resistive damping between a loudspeaker and an amplifier.
Many amplifier and loudspeaker systems endeavor to enhance quality by using frequency cross-over circuits and other signal frequency enhancing components, as is well known. However such additional circuits include reactive components, such as coils and capacitors, that also create their own back EMF, giving rise to additional problems for faithful reproduction of sound by the loudspeaker in the system. For example, U.S. Pat. No. 4,475,233 that issued on Oct. 2, 1984 to Wadkins shows an effort to dampen the reactive components of traditional frequency cross-over and frequency shaping circuits by the provision of damping resistors connected in shunt with the reactive components of the circuits.
Additionally, speaker damping requirements vary with frequency of the current generated by the amplifier, and with mechanical characteristics of the loudspeaker, and no known amplifier loudspeaker systems have adequately solved variable damping problems. In each amplifier loudspeaker system, three forms of damping must be addressed. Acoustic damping refers to damping of the speaker by sound waves generated within a cabinet containing the loudspeaker that tend to effect motion of the speaker in response to sound waves generated by motion of the speaker as it is driven by the current from the amplifier. Mechanical damping refers to impact on motion of the speaker through materials and apparatus that suspend the speaker within a mounting housing for securing the speaker to the cabinet. For example, a typical high fidelity loudspeaker has a metal housing that surrounds, partially encases, and supports a moveable cone of the speaker, and that also supports a magnet that drives the loudspeaker cone. Variations in the materials suspending the cone to the metal housing will impact mechanical damping of the speaker resulting in variations in sound reproduction that are a function of the mechanical damping. Electrical damping refers to the back EMF current generated within the magnet and coil of the speaker that occurs as the cone of the speaker continues movement by inertia after being driven in response to a current from the amplifier. No known technology effectively achieves total damping of all aforesaid sources of damping across a working frequency range of the loudspeaker and amplifier system.
The invention is a variable damping circuit for a loudspeaker that provides for frequency dependent control of a loudspeaker by an amplifier. The variable damping circuit includes an amplifier, at least one loudspeaker, a pair of connectors between the amplifier and the loudspeaker, and a reactive component wired in parallel with a resistor and connected to one of the pair of connectors between the amplifier and loudspeaker, wherein the total resistance value of the reactive component and resistor combined does not exceed fifty percent of a resistance value of the loudspeaker. In a first preferred embodiment, the reactive component is a coil. In a second preferred embodiment, the reactive component is a capacitor, and, in a third preferred embodiment, both the coil and the capacitor are connected in parallel with the resistor.
The resistance value of the coil and/or capacitor changes in response to a frequency of a current passing through the reactive component and resistor. The change in resistance value of the reactive component is tempered by the resistor in parallel with the reactive component such that the highest value obtainable by the reactive component and resistor combined is less than that of the resistor, and the lowest value will be less than the resistance value of the reactive component. Because of the aforesaid total resistance values of the coil and/or of the capacitor, the combination of the reactive component in parallel with the resistor imparts only a negligible change in voltage or power delivered to the loudspeaker from the amplifier. Therefore, the variable damping circuit serves to tune the loudspeaker by dynamically altering the total damping factor produced by the loudspeaker without impeding the amplifier current or artificially shaping the frequency of the current delivered by the amplifier to the loudspeaker. By controlling the effective resistance between the amplifier and loudspeaker to be a function of the frequency of a back EMF current passing through the reactive component and the resister instead of attempting to eliminate the back EMF, the variable damping circuit utilizes the back EMF to variably tune the loudspeaker at all frequencies of amplifier current and loudspeaker. Therefore, the loudspeaker and amplifier are precisely coupled to optimize a total damping across a working frequency range of the loudspeaker with a lowest possible distortion.
Accordingly, it is a general object of the present invention to provide variable damping circuit for a loudspeaker that overcomes deficiencies of prior art loudspeaker damping circuits.
It is a more specific object to provide a variable damping circuit for a loudspeaker that enables a loudspeaker to be tuned to an amplifier utilizing the back electromotive force (xe2x80x9cEMFxe2x80x9d) current as a means of control.
It is yet another object to provide a variable damping circuit for a loudspeaker that provides for frequency dependent damping of the loudspeaker by utilizing the back EMF.
It is still a further object to provide a variable damping circuit for a loudspeaker that optimizes a total damping across a working frequency range of an amplifier current supplied to the loudspeaker.
These and other objects and advantages of this invention will become more readily apparent when the following description is read in conjunction with the accompanying drawings.